Virology lecture 2 (viral structure)

http://www.virology.ws

VIRAL STRUCTURE & CLASSIFICATION
S144 Lecture 2 (Virology)
Marilen M. Parungao-Balolong
Reference: Chapter 3 Carter And Saunders, 2007)

Thursday, June 30, 2011

SKILLS, VALUES, OUTPUTS

✤ Listening, Writing and
Oral Communication winfoin.com

Skills
✤ Critical Analysis and
Organization of Ideas
✤ Appreciate Importance
of Viral Structure
Marilen M. Parungao-Balolong 2011 Reference: Chapter 3 Carter And Saunders, 2007)

LECTURE OUTLINE

✤ Recall: Viruses
Introduction
✤ Structure of Viruses
✤ Functional Anatomy
✤ Classiﬁcation


REFERENCES

✤ Carter and Saunders, 2007 (Chapter 3)
✤ Gelderblom, 2010 (Chapter 41)
✤ (Bookshelf ID: NBK8174 PMID: 21413309)
✤ http://www.ncbi.nlm.nih.gov/books/NBK8174/


VIRUSES: INTRODUCTION

✤ Viruses are small
obligate intracellular
parasites
✤ Contain either a
RNA or DNA
genome surrounded
by a protective,
virus-coded protein
coat

VIRUSES: INTRODUCTION

✤ Viruses may be viewed as mobile genetic elements, most probably of
cellular origin and characterized by a long co-evolution of virus and
host

bio3400.nicerweb.net


VIRUS: INTRODUCTION

✤ Propagation
depend on
specialized host
cells supplying
the complex
metabolic and
biosynthetic
machinery of
eukaryotic or ncbi.nlm.nih.gov

prokaryotic cells

LECTURE OUTLINE

✤ Recall: Viruses
Introduction
✤ Structure of Viruses virology.ws

✤ Classiﬁcation
medical-dictionary.thefreedictionary.com


Reference: Chapter 3 Carter And Saunders, 2007)

Marilen M. Parungao-Balolong 2011 dvm5.blogspot.com

CORONAVIRUS STRUCTURE:
SARS

http://learn.genetics.utah.edu/archive/sars/index.html

THE CORE:
GENOME
Copyright © 1996, The University of Texas Medical Branch at Galveston.

✤ Except in helical
nucleocapsids, little is
known about the
packaging or
organization of the viral
genome within the core

✤ SMALL VIRIONS:

✤ simple nucleocapsids

✤ containing 1 to 2
protein species

THE CORE:
GENOME

✤ LARGE VIRIONS:
✤ nucleic acid
genome
complexed with
basic protein(s)
✤ protected by a
single- or double
layered capsid or
by an envelope

CHEMICAL COMPOSITION OF
GENOME

✤ The genome of a virus may consist of DNA or RNA,
which may be single stranded (ss) or double stranded
(ds), linear or circular
✤ The entire genome may occupy either one nucleic acid
molecule (monopartite genome) or several nucleic acid
segments (multipartite genome)
✤ The different types of genome necessitate different
replication strategies

INTRODUCTION TO VIRUS
STRUCTURE
✤ TYPES OF VIRION STRUCTURE
TYPES GENOMES

dsDNA ssDNA dsRNA ssRNA

Icosahedral
(naked)
Icosahedral
(Enveloped)

Helical (naked)

Helical
(Enveloped)


http://www.mansﬁeld.ohio-state.edu/~sabedon/017vrgnm.gif


VIRUS GENOMES

✤ dsDNA
✤ encode their genes in the same kind of
molecule as animals, plants, bacteria and
other cellular organisms
✤ ssDNA, dsRNA, ssRNA
✤ unique to viruses

ARRANGEMENT OF GENOME

GENOME EXAMPLE
ssDNA, linear Parvovirus
dsDNA, linear Poxvirus
ssDNA, circular Phage X174
dsDNA, circular Baculoviruses
ssRNA, linear Tobacco Mosaic Virus
dsRNA, linear Reovirus
ssRNA, circular Hepatitis D virus
Note: there are no viruses known with circular dsRNA genomes

USUALLY....

✤ FUNGI VIRUSES
✤ dsRNA sdnhm.org
topnews.in

✤ PLANT VIRUSES http://
www.whmsoft.net

✤ ssRNA
✤ PROKARYOTIC VIRUSES
✤ dsDNA

POINTS TO REMEMBER...

✤ Some linear molecules may be in a
circular conformation as a result of base
pairing between complimentary
sequences at their ends
✤ Example:
✤ DNA in Hepadnavirus
✤ RNA in Inﬂuenza virions

THE CAPSID: PROTEIN CORE

virology.ws medical-dictionary.thefreedictionary.com

Take note of the nucleocapsid and envelope

THE CAPSID: PROTEIN CORE

Structure of adenovirus. The icosahedral capsid structure of
adenovirus is made up of three proteins, hexon, penton
base, and fiber. A cross-sectional view of the viral capsid.
Some proteins are associated with viral DNA, whereas
others are associated with hexon and are involved in the
formation of the capsid.


MORPHOLOGY : Helical

✤ Helical morphology is seen in
nucleocapsids of many
ﬁlamentous and pleomorphic
viruses

✤ Helical nucleocapsids consist
of a helical array of capsid
proteins (protomers) wrapped
around a helical ﬁlament of
nucleic acid The helical structure of the rigid tobacco mosaic virus rod




✤ In the replication of viruses
with helical symmetry,
identical protein subunits
(protomers) self-assemble
into a helical array
surrounding the nucleic
acid, which follows a
similar spiral path

✤ Nucleocapsids form rigid,
highly elongated rods or
ﬂexible ﬁlaments


✤ Details of the capsid
structure are often
discernible by electron
microscopy

✤ NOTE: Helical
nucleocapsids are
characterized by length, Fragments of flexible helical nucleocapsids (NC) of Sendai
virus, a paramyxovirus, are seen either within the protective
envelope (E) or free, after rupture of the envelope
width, pitch of the helix, and
number of protomers per
helical turn

MORPHOLOGY

✤ Icosahedral
morphology is
characteristic of
the
nucleocapsids of
many
“spherical”
viruses


MORPHOLOGY

✤
Lines through opposite
vertices define axes of fivefold
rotational symmetry: all
structural features of the
polyhedron repeat five times
within each 360° of rotation
about any of the fivefold axes

✤
Lines through the centers of
opposite triangular faces form
axes of threefold rotational
symmetry; twofold rotational
symmetry axes are formed by
lines through midpoints of Icosahedral models seen, left to right, on fivefold,
opposite edges. threefold, and twofold axes of rotational symmetry



MORPHOLOGY

✤ Viruses were ﬁrst
found to have 532
symmetry by x-ray
diffraction studies
✤ Electron
microscopy with Adenovirus after negative stain electron microscopy

negative-staining Copyright © 1996, The University of Texas Medical Branch at Galveston.

techniques


MORPHOLOGY

✤ PROTOMERS:

✤ structural polypeptide
chains

✤ arranged in oligomeric
clusters (capsomeres)

✤ readily delineated by
negative staining Adenovirus after negative stain electron microscopy

electron microscopy Copyright © 1996, The University of Texas Medical Branch at Galveston.

✤ form the closed capsid
shell

pc.maricopa.edu
THE CAPSOMERES


CAPSOMERES & ENVELOPE

✤ The number and
arrangement of the
capsomeres are useful
in identiﬁcation and
classiﬁcation
✤ Many viruses also
have an outer Envelope of
envelope Herpesvirus
biologie.uni-hamburg.de


CAPSID & ENVELOPE

pc.maricopa.edu


✤ Envelope consists of a
lipid bilayer with proteins
(usually glycoproteins)
imbedded in it THE ENVELOPE
✤ Lipids derived from
host cell

✤ Proteins encoded by the
virus

✤ Envelope is important in
determining host cell
speciﬁcity & some aspects
of cell penetration are
affected by it

ENVELOPED VIRUSES


COMPLEX VIRUSES


LECTURE OUTLINE

✤ Recall: Viruses
Introduction
✤ Structure of Viruses
bbc.co.uk
✤ Classiﬁcation


STRUCTURE IN RELATION TO
FUNCTION

✤ Core

! ! ! a.! DNA or RNA
! ! ! b.! Contains genetic
information
ncbi.nlm.nih.gov
!!


FUNCTION sparknotes.com

✤ Capsid

! ! ! a.! Outer protein coat

! ! ! b.! Functions

! ! ! ! 1).!Protects core

! ! ! ! 2).!Shape of the virus

! ! ! ! 3).!Attachment to host

cell membrane (by means of

spikes) library.thinkquest.org


FUNCTION

✤ Envelope

✤ Membrane around capsid - enveloped virus

✤ Not all viruses have envelope

✤ If lack envelope - naked virus!

✤ Composed of:

✤ Bilayer of phospholipids and proteins microscopicblog.blogspot.com

✤ Derived from host bell membrane during viral multiplication

FUNCTION me-you-and-virus.blogspot.com

wpro.who.int
✤ Functions :

✤ Protection from drying (enhances
transmission)

✤ Makes virus more susceptible to
chemical agents that dissolve lipids

✤ Attachment to host cell membrane
(by means of spikes)


✤ Viruses are grouped on the basis of size and shape, chemical
composition and structure of the genome, and mode of replication


PLANT VIRUSES

Marilen M. Parungao-Balolong 2011 Reference: Chapter 13 TortoraMicrobiology

CLASSIFYING ENVELOPED
VIRUS BASED ON SHAPE...

✤ Sphere (eg. Inﬂuenza
virus)
✤ Bullet (e.g. Rabies
virus)
✤ Rod (e.g. Baculovirus)
✤ Thread (e.g Ebola
virus)

CLASSIFYING VIRUS BASED
ON GENOME...

antiviralintelistrat.com


END OF LECTURE 2

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Virology lecture 2 (viral structure)

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